The inventors of the present invention have proposed delaminatable laminated bottles of the aforesaid type as disclosed in the following patent publications 1 to 6.    Patent Publication 1: JP2001-146260-A    Patent Publication 2: JP2001-114328-A    Patent Publication 3: JP2001-105477-A    Patent Publication 4: JP2001-105478-A    Patent Publication 5: JP2001-146260-A    Patent Publication 6: JP2002-263166-A
These prior art delaminatable laminated bottles do not require post-processing such as melt-processing or piercing for forming an air introduction hole in an outer later after injection molding of a preform, because the formation of the air introduction hole is achieved with the use of a pin provided in a mold. This is advantageous in that the molding process is simplified and the production is achieved by utilizing an existing production plant which is modified simply by providing the pin in the mold, thereby reducing plant costs. Without the need for the post-processing, there is no possibility of contamination of products with foreign matters due to the post-processing, so that these delaminatable laminated bottles are advantageously utilized particularly as cosmetic containers and medical containers such as eyedroppers. In the prior art delaminatable laminated bottles, a check valve for preventing back flow of air in the air introduction hole is defined by an inner layer mouth portion, thereby achieving simplification of the construction and reduction of the costs.
In order to ensure the functions of the delaminatable laminated bottle and prevent distribution of defective products, it is supposedly important to check for assured formation of the air introduction hole. However, there is no established check method. Particularly for the molding of a small bottle having a volume of about 10 ml, high levels of accuracies are required in various aspects. Therefore, it is primarily important to establish a defect check method.
Where the prior art is applied to a small eyedropper having a volume of about 10 ml and the inner layer of the eyedropper has a thickness sufficient for proper functioning, the ratio of the inner layer thickness to a mouth diameter is increased. Hence, there is a possibility that the inner layer does not properly function as the check valve. Further, where the introduction hole is formed in a bottle body, the introduction hole is liable to be closed when the bottle body is drawn in a blow molding process. Therefore, it is desirable to establish the check method.